In the UMTS (Universal Mobile Telecommunications System) network, for the purposes of improving spectral efficiency and improving the data rates, system features based on W-CDMA (Wideband Code Division Multiple Access) are maximized by adopting HSDPA (High Speed Downlink Packet Access) and HSUPA (High Speed Uplink Packet Access). For this UMTS network, for the purposes of further increasing high-speed data rates, providing low delay and so on, long-term evolution (LTE) has been under study (non-patent literature 1).
In the third-generation system, it is possible to achieve a transmission rate of maximum approximately 2 Mbps on the downlink by using a fixed band of approximately 5 MHz. Meanwhile, in the LTE system, it is possible to achieve a transmission rate of about maximum 300 Mbps on the downlink and about 75 Mbps on the uplink by using a variable band that ranges from 1.4 MHz to 20 MHz. Furthermore, in the UMTS network, for the purpose of achieving further broadbandization and higher speed, successor systems of LTE have been under study (for example, LTE-Advanced (LTE-A)). The system band of the LTE-A system includes at least one component carrier (cell), where the system band of the LTE system is one unit. Widening the band by way of aggregating a plurality of component carriers in this way is referred to as “carrier aggregation.”
In radio communication, as uplink and downlink duplexing methods, there are frequency division duplexing (FDD) to divide the uplink and the downlink by frequency and time division duplexing (TDD) to divide the uplink and the downlink by time. In Release-10 LTE, when carrier aggregation is executed in TDD, as shown in FIG. 1A, the ratio of uplink subframes and downlink subframes (Transmission Time Intervals: TTIs) is the same in all component carriers. In Release-11 LTE, considering application of a heterogeneous network and so on, as shown in FIG. 1B, changing the ratio of uplink subframes and downlink subframes in each component carrier when carrier aggregation is executed in TDD, is under study.
Meanwhile, when broadbandization is achieved by way of increasing the number of component carriers (the number of carrier aggregations) to use for communication between a radio base station apparatus and a user terminal, as shown in FIG. 2, for example, it is possible to multiplex and transmit downlink control information (DCI 2) for the downlink shared channel to be transmitted by a component carrier CC 2 (S-cell (Secondary-cell)) on the downlink control channel (PDCCH) of another component carrier CC 1 (P-cell (Primary-cell)) (cross-carrier scheduling). Here, a DCI configuration, in which a carrier indicator (CI) is added in order to identify which component carrier (CC 1 or CC 2) the information of the downlink control information (DCI 2) relates to, is adopted. The field to represent the carrier indicator (CI) is the CIF. That is to say, when DCI for shared data channel demodulation to be multiplexed on the data field of a given component carrier is multiplexed over the control channel field of another component carrier, a CIF to represent the index of the component carrier (carrier index) where the shared data channel to be demodulated is multiplexed, is added to the DCI.